A voltage range of energy sources, such as batteries, fuel cells, etc., for portable electronic devices tends to broaden and a minimum voltage of the range tends to go further down. Contemporaneously, portable electronic devices comprise many electronic components and circuits which need for optimum operation a supply voltage adjusted for their specific purposes.
Mobile communication devices such as mobile phones and portable communication terminals employ batteries, e.g. lithium ion batteries or the like, as their input power source. In mobile phones the battery supplies power through electronic circuitry to a load, e.g. a high frequency power amplifier in connection with a transmitter/transceiver. A powerful signal generated and transmitted by the wireless transmitter/transceiver draws more power from the battery than when a lower power signal is generated and transmitted. In the power amplifiers the operating voltage is selected in a technical sense so that the gain of the transmitter is adjusted so as to not transmit a RF signal more powerful than necessary for adequate communications. To do this, the power supply from the battery to the load is typically managed by the electronic circuitry comprising a switching regulator which is controlled by a control circuit to adjust the operating voltage for the power amplifier in the transmitter/transceiver.
A switching regulator used in battery-driven equipment is typically a DC-to-DC converter which converts battery voltages into the various voltages required by the supplied device. The DC-to-DC converter changes the DC energy from one level to another by changing the input energy into a different impedance level. The DC-to-DC converter provides a regulated output voltage based upon an input voltage and can generate output voltages higher or lower than the input voltage. Today, switched mode power supplies (SMPS) have gained popularity as DC-to-DC converters in battery-driven electronic devices because their efficient design meets well the size and power requirements of such devices.
The output voltage of the battery is called here a battery voltage and the voltage to supply a load is referred to as a supply voltage. The battery gives the battery voltage within a predetermined variation range between a minimum and maximum battery voltage. The supply voltage is fed to the load within a predetermined variation range between a minimum and maximum supply voltage.
There is a trend that for example future lithium based batteries will have a battery voltage range from approximately two volts to 4.5 volts. This means that the battery gives from the maximum battery voltage of 4.5 volts (when in charge) to the minimum battery voltage of close to 2 volts. This will bring about a challenge how to manage an appropriate power supply for some electronic circuits used in mobile communication devices. For example, as well known it is very challenging to design a high frequency power amplifier (PA) for supply voltages at close range to two volts. One solution for this has been to use a high efficiency DC-to-DC converter, e.g. a switched mode power supply (SMPS), to regulate the supply voltage just below the minimum battery voltage. But in addition to design complexity this solution brings another drawback, namely it will lead to efficiency loss in the energy conversion. Another solution has been to convert the supply voltage at close range of above 4.5 volts. The drawback of this solution is that the voltages at close range to above 4.5 volts are too close to the maximum voltages of the semiconductor processes designed for use in future power amplifier manufacturing. Then, the optimum choice for a supply voltage to the power amplifier would be in the range of 3 to 4 volts.
In prior art the solutions mentioned above have been accomplished mostly by the following three means. Firstly, a lower than minimum battery voltage of the same polarity is used for all mobile phone functions by means of linear regulators. Secondly, the DC-to-DC converter converts the whole battery voltage range to a voltage of the same polarity but lower than the minimum battery voltage of the battery voltage range or higher than the maximum battery voltage of the battery voltage range. Thirdly, the DC-to-DC converter converts the whole battery voltage range to a voltage of the same polarity within the battery voltage range.
The optimum supply voltage range of 3 to 4 volts for supplying the power amplifier by the above-mentioned means provides that the DC-to-DC converter should operate in two modes, namely stepping up and stepping down, depending on the battery's charge state. Thus the step-up and step-down converters are used. When the battery voltage is higher than the supply voltage required by the load including the power amplifier, the voltage is set to a predetermined supply voltage by the stepdown operation mode. When the battery voltage is decreased and becomes lower than the supply voltage required by the load including the power amplifier, the voltage is set to a predetermined supply voltage by the step-up operation mode.
In prior art solutions to provide a desired supply power range there are problems caused by the DC-to-DC converters capable of a two-mode operation depending on the battery's respective charge state. Problems will arise due to delay in switching between step-up mode and step-down mode, because there is a danger for oscillation between these modes. This oscillation danger is particularly relevant when the supply voltage needs to be modulated in the power amplifiers for envelope restoration (ER) transmitter solutions. Further the use of these types of DC-to-DC converters such as step-up and step-down converters leads to higher cost and component count, as well as poorer efficiency which shortens the use time of the battery.
As battery-driven portable communication devices such as mobile phones are considered to be proceeding toward being more multi-functioning electronic devices with each passing year, there will arise a problem caused by the complexity of the power supply circuitry according to prior art. To configure the power supply circuitry capable of performing the complex control by using standard electronic parts, will increase the number of parts and reduce the packaging density. For its part, this causes problems in reducing the size of the battery-driven electronic devices which objective is particularly emphasized on the design of mobile phones and other wireless communication terminals.
The problems set forth above are overcome by providing a power supply circuit for a battery-driven mobile communication device, which is capable of supplying voltage within an optimum supply voltage range to the load continuously without any mode change according to the embodiments of the present invention.